1.0 Introduction
Respiratory devices typically include a flexible conduit to convey a breathing gas such as air to a patient. Generally, the conduit should be strong enough to prevent crushing or kinking, as such could cause occlusions in the conduit thereby restricting or blocking the delivery of breathing gas.
1.1 General Structure
One known conduit structure includes a hard plastic or metal spiral reinforcement around the inside or outside of a thin-walled flexible plastic tube. This helical or spiral structure supports the tube and prevents occlusions. Preferably, the spiral is wound around the outside of the plastic tube so that the conduit maintains a smooth bore, such as in Smooth-Bore tubing.
1.2 Heat Transfer
Humidified breathing gas may be delivered to a patient as part of their respiratory therapy. In this case, it is advantageous to minimise head transfer out of the conduit in order to avoid condensation of the humidified gas as it flows through the conduit. The condensation problem is particularly pronounced in cold environments.
Plastics and metals are not efficient thermal insulators. Therefore, in order to prevent condensation, additional structure may be added to the conduit. For example, an insulating sleeve may be used to cover the conduit and provide insulation. Another proposed solution involves using a heated wire to heat the conduit (Thermo-Smart® by Fisher & Paykel Healthcare). Actively heating the tube may result in the air temperature rising as it travels along the tube which in turn will result in the air drying out. Smooth-Bor™ also produces a dual-walled conduit that provides added insulation.
1.3 Weight
Present conduits can also be heavy causing an uncomfortable resistance to patient head movements. Additional items, such as an insulating sleeve, added to the conduit may cause the overall weight to increase. Additional items may also increase the friction of the conduit against surrounding items, such as bed linen.